/**
 *    Copyright (C) 2014 MongoDB Inc.
 *
 *    This program is free software: you can redistribute it and/or  modify
 *    it under the terms of the GNU Affero General Public License, version 3,
 *    as published by the Free Software Foundation.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    GNU Affero General Public License for more details.
 *
 *    You should have received a copy of the GNU Affero General Public License
 *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 *    As a special exception, the copyright holders give permission to link the
 *    code of portions of this program with the OpenSSL library under certain
 *    conditions as described in each individual source file and distribute
 *    linked combinations including the program with the OpenSSL library. You
 *    must comply with the GNU Affero General Public License in all respects for
 *    all of the code used other than as permitted herein. If you modify file(s)
 *    with this exception, you may extend this exception to your version of the
 *    file(s), but you are not obligated to do so. If you do not wish to do so,
 *    delete this exception statement from your version. If you delete this
 *    exception statement from all source files in the program, then also delete
 *    it in the license file.
 */

#pragma once

#include "mongo/db/diskloc.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/storage/mmap_v1/btree/key.h"

namespace mongo {

    const int OldBucketSize = 8192;

    //
    // On-disk index format
    //

#pragma pack(1)
    /**
     * This is the fixed width data component for storage of a key within a bucket.  It contains an
     * offset pointer to the variable width bson data component.  This may be 'unused', please see
     * below.
     *
     * Why is this templated on Loc?  Because V0 and V1 have different size DiskLoc(s) but otherwise
     * the same layout.
     */
    template <class LocType>
    struct FixedWidthKey {
        //
        // Data
        //

        /**
         * The 'left' child bucket of this key.  If this is the i-th key, it points to the i index
         * child bucket.
         */
        LocType prevChildBucket;

        /**
         * The location of the record associated with this key.
         */
        LocType recordLoc;

        /**
         * Offset within current bucket of the variable width bson key for this _KeyNode.
         */
        unsigned short _kdo;

        //
        // Accessors / mutators
        //

        short keyDataOfs() const {
            return static_cast<short>(_kdo);
        }

        void setKeyDataOfs(short s) {
            _kdo = s;
            invariant(s>=0);
        }

        void setKeyDataOfsSavingUse(short s) {
            // XXX kill this func
            setKeyDataOfs(s);
        }

        /**
         * Unused keys are not returned by read operations.  Keys may be marked
         * as unused in cases where it is difficult to delete them while
         * maintaining the constraints required of a btree.
         *
         * Setting ofs to odd is the sentinel for unused, as real recordLoc's
         * are always even numbers.  Note we need to keep its value basically
         * the same as we use the recordLoc as part of the key in the index
         * (to handle duplicate keys efficiently).
         *
         * Flagging keys as unused is a feature that is being phased out in favor
         * of deleting the keys outright.  The current btree implementation is
         * not expected to mark a key as unused in a non legacy btree.
         */
        void setUnused() {
            recordLoc.GETOFS() |= 1;
        }

        void setUsed() { recordLoc.GETOFS() &= ~1; }

        int isUnused() const {
            return recordLoc.getOfs() & 1;
        }

        int isUsed() const {
            return !isUnused();
        }
    };

    /**
     * This structure represents header data for a btree bucket.  An object of
     * this type is typically allocated inside of a buffer of size BucketSize,
     * resulting in a full bucket with an appropriate header.
     *
     * The body of a btree bucket contains an array of _KeyNode objects starting
     * from its lowest indexed bytes and growing to higher indexed bytes.  The
     * body also contains variable width bson keys, which are allocated from the
     * highest indexed bytes toward lower indexed bytes.
     *
     * |hhhh|kkkkkkk--------bbbbbbbbbbbuuubbbuubbb|
     * h = header data
     * k = KeyNode data
     * - = empty space
     * b = bson key data
     * u = unused (old) bson key data, that may be garbage collected
     */
    struct BtreeBucketV0 {
        /**
         * Parent bucket of this bucket, which isNull() for the root bucket.
         */
        DiskLoc parent;

        /**
         * Given that there are n keys, this is the n index child.
         */
        DiskLoc nextChild;

        /**
         * Can be reused, value is 8192 in current pdfile version Apr2010
         */
        unsigned short _wasSize;

        /**
         * zero
         */
        unsigned short _reserved1;

        int flags;

        /** basicInsert() assumes the next three members are consecutive and in this order: */

        /** Size of the empty region. */
        int emptySize;

        /** Size used for bson storage, including storage of old keys. */
        int topSize;

        /* Number of keys in the bucket. */
        int n;

        int reserved;

        /* Beginning of the bucket's body */
        char data[4];

        // Precalculated size constants
        enum { HeaderSize = 40 };
    };

    // BtreeBucketV0 is part of the on-disk format, so it should never be changed
    BOOST_STATIC_ASSERT(
        sizeof(BtreeBucketV0) - sizeof(reinterpret_cast<BtreeBucketV0*>(NULL)->data) 
                == BtreeBucketV0::HeaderSize);

    /**
     * A variant of DiskLoc Used by the V1 bucket type.
     */
    struct DiskLoc56Bit {
        //
        // Data
        //

        int ofs;

        unsigned char _a[3];

        //
        // Accessors XXX rename these, this is terrible
        //

        int& GETOFS()      { return ofs; }

        int getOfs() const { return ofs; }

        //
        // Comparison
        //

        bool isNull() const { return ofs < 0; }

        unsigned long long toLongLong() const { 
            // endian
            unsigned long long result = ofs;
            char* cursor = reinterpret_cast<char *>(&result);
            *reinterpret_cast<uint16_t*>(cursor + 4) = *reinterpret_cast<const uint16_t*>(&_a[0]);
            *reinterpret_cast<uint8_t*>(cursor + 6) = *reinterpret_cast<const uint8_t*>(&_a[2]);
            *reinterpret_cast<uint8_t*>(cursor + 7) = uint8_t(0);
            return result;
        }

        bool operator<(const DiskLoc56Bit& rhs) const {
            // the orderering of dup keys in btrees isn't too critical, but we'd like to put items
            // that are close together on disk close together in the tree, so we do want the file #
            // to be the most significant bytes
            return toLongLong() < rhs.toLongLong();
        }

        int compare(const DiskLoc56Bit& rhs) const {
            unsigned long long a = toLongLong();
            unsigned long long b = rhs.toLongLong();
            if ( a < b ) {
                return -1;
            }
            else {
                return a == b ? 0 : 1;
            }
        }

        bool operator==(const DiskLoc56Bit& rhs) const {
            return toLongLong() == rhs.toLongLong();
        }

        bool operator!=(const DiskLoc56Bit& rhs) const {
            return toLongLong() != rhs.toLongLong();
        }

        bool operator==(const DiskLoc& rhs) const {
            return DiskLoc(*this) == rhs;
        }

        bool operator!=(const DiskLoc& rhs) const {
            return !(*this==rhs);
        }

        //
        // Mutation
        //

        enum { 
            // first bit of offsets used in _KeyNode we don't use -1 here.
            OurNullOfs = -2
        };

        void Null() { 
            ofs = OurNullOfs; 
            _a[0] = _a[1] = _a[2] = 0;
        }

        void operator=(const DiskLoc& loc);

        //
        // Type Conversion
        //

        operator const DiskLoc() const { 
            // endian
            if( isNull() ) return DiskLoc();
            unsigned a = *((unsigned *) (_a-1));
            return DiskLoc(a >> 8, ofs);
        }

        std::string toString() const { return DiskLoc(*this).toString(); }
    };

    struct BtreeBucketV1 {
        /** Parent bucket of this bucket, which isNull() for the root bucket. */
        DiskLoc56Bit parent;

        /** Given that there are n keys, this is the n index child. */
        DiskLoc56Bit nextChild;

        unsigned short flags;

        /** Size of the empty region. */
        unsigned short emptySize;

        /** Size used for bson storage, including storage of old keys. */
        unsigned short topSize;

        /* Number of keys in the bucket. */
        unsigned short n;

        /* Beginning of the bucket's body */
        char data[4];

        // Precalculated size constants
        enum { HeaderSize = 22 };
    };

    // BtreeBucketV1 is part of the on-disk format, so it should never be changed
    BOOST_STATIC_ASSERT(
        sizeof(BtreeBucketV1) - sizeof(reinterpret_cast<BtreeBucketV1*>(NULL)->data) 
                == BtreeBucketV1::HeaderSize);

    enum Flags {
        Packed = 1
    };

    struct BtreeLayoutV0 {
        typedef FixedWidthKey<DiskLoc> FixedWidthKeyType;
        typedef DiskLoc LocType;
        typedef KeyBson KeyType;
        typedef KeyBson KeyOwnedType;
        typedef BtreeBucketV0 BucketType;

        enum { BucketSize = 8192,
               BucketBodySize = BucketSize - BucketType::HeaderSize 
        };

        // largest key size we allow.  note we very much need to support bigger keys (somehow) in
        // the future.

        static const int KeyMax = OldBucketSize / 10;

        // A sentinel value sometimes used to identify a deallocated bucket.
        static const int INVALID_N_SENTINEL = -1;

        static void initBucket(BucketType* bucket) {
            bucket->_reserved1 = 0;
            bucket->_wasSize = BucketSize;
            bucket->reserved = 0;
        }
    };

    struct BtreeLayoutV1 {
        typedef FixedWidthKey<DiskLoc56Bit> FixedWidthKeyType;
        typedef KeyV1 KeyType;
        typedef KeyV1Owned KeyOwnedType;
        typedef DiskLoc56Bit LocType;
        typedef BtreeBucketV1 BucketType;

        enum { BucketSize = 8192 - 16,  // The -16 is to leave room for the Record header
               BucketBodySize = BucketSize - BucketType::HeaderSize 
        };

        static const int KeyMax = 1024;

        // A sentinel value sometimes used to identify a deallocated bucket.
        static const unsigned short INVALID_N_SENTINEL = 0xffff;

        static void initBucket(BucketType* bucket) { }
    };

#pragma pack()

}  // namespace mongo
